Medical electrical leads are configured for pacing, sensing, cardioversion, and defibrillation therapies. Leads attach to tissue through active fixation (e.g. tines etc.) or passive fixation (e.g. adhesive). Exemplary medical electrical devices with tines, comprising nickel titanium (Nitinol), are known in the art, as shown and described in U.S. Pat. No. 4,505,767 to Quinn, U.S. Pat. No. 5,067,957 to Jervis, U.S. Pat. No. 7,650,186 to Hastings et al. and US Pregrant Publication No. 2012-0172892 A1 filed Apr. 28, 2011 to Grubac et al. Delivery of therapy is dependent upon the lead tines staying attached to the cardiac tissue. Occasionally, a lead can dislodge from its position which is problematic since therapy cannot be delivered to the tissue. Lead tines can be designed to be securely attached to tissue in a manner that the lead will not dislodge; however, perforations of the heart wall can increase. Perforations occur when tines completely pierce or penetrate the heart wall that comprises three layers—endocardium, myocardium and epicardium. Each heart wall layer possesses different tissue properties. For example, the epicardium is harder than the thicker softer myocardium while the myocardium is softer than the endocardium. Since each heart wall layer possesses different tissue properties, tines pass through each layer at a different rate of speed. Consequently, reduced dislodgement of tines must be balanced against reduction of perforations by tines.
Typically, to address this issue, lead tines have been designed based upon a push force applied by user that is translated to the tines. It is desirable to develop tines, on a medical device, that does not merely rely on the force applied by the tines but rather eliminates dislodgement while substantially reducing perforations during implanting of a medical device.